where dx is the distance between the H alpha and H beta lines measured in pixels along the horizontal axis in a raw image. Try to find the distance to the nearest pixel (the reading of the mouse pointer is sufficient). In the example, the H alpha line is at x = 882, while the H beta line is at x = 535. So dx = 882-534 = 347, and thus the pixel size to adopt is p = 3123/347 = 9.00 pixels."

Robin Leadbeater wrote:Have you calculated the pixel size to use ? (This is not the same as the actual pixel size)

Thank you very much RobinI knew that but .... I forgot it!by doing that I find 5.224 instead of 5.4 and that changes everythingIsis finds all the Balmer raysfor the lines of the calibration module by cons it is always the samethanks to you, I'm moving forward!

as you will have guessed, I do not speak English, it's google that translates